1. Field of the Invention
The present invention relates to medical monitoring systems and, in particular, to a highly portable, non-invasive, physiological monitoring system for alerting a caregiver that a patient is in need of medical assistance.
2. Discussion of the Prior Art
In the medical monitoring area, multi-channel patient monitors are currently available such as those manufactured by Hewlett-Packard Company of Palo Alto, Calif. These monitors are hard-wired between the patient-worn sensors and the processing/display module. They are bulky and unsuitable for less than intensive, critical care monitoring. These bedside and console monitors offer multiparameter sensing, but are not intended to be worn directly by the patient. They do not offer a nurse paging feature, but instead require constant monitoring by an attendant.
The Hewlett-Packard devices include telemetric modules which provide ECG telemetric data. The Hewlett-Packard model 78100A/78101A are a transmitter and receiver system by which a ECG signal, derived from a set of sensors worn by the patient, is transmitted to remote monitoring equipment. The receiver in such a system is intended to be placed on a table top and not to be worn by the caregiver. Thus, the caregiver must remain in visual or audio contact with the receiver unit at all times.
A unit offered by Lifeline Systems Inc. of Watertown, Mass. include a subscriber worn help button and a receiver positioned within a 200 foot vicinity of the subscriber. When the subscriber presses the help button, the receiver makes a call on the telephone line to an emergency response center where it is acted upon. The system includes a timer which requires that the user reset it manually. In absence of such a reset, an alarm is automatically sent out indicating that the user is unable to call for help. Such a system requires user intervention and also is not capable of providing a real time alarm when the user is unable to call for help. Further, the ability of the system to get through to the emergency response center, or to a caregiver, in the event of an emergency is a function of the reliability of the telephone system. Further, even if the alarm is received and responded to, such help may not be forthcoming for several minutes which could be critical to the survival of the patient being monitored.
It would therefore be desirable to have a system which can be worn by the subject being monitored and which can provide alarm indications to caregivers in the immediate vicinity of the subject being monitored, as well as to remote caregivers, and which also is capable of detecting alarm conditions separate and apart from manual activation of the system by the subject being monitored. It would also be desirable to have a system which has redundant transmission paths to insure that caregivers are summoned in an expedient manner.
Conventional practice for diagnosing sleep disorders requires that the patient be admitted to a "sleep lab". Typically, these sleep labs are located at hospitals or clinics and consist of a special in-patient unit equipped with a complicated array of cumbersome polysomnograph equipment. The patient is required to sleep in the unit while being monitored by a combination of bulky, uncomfortable sensors which are attached to various parts of the body. Obviously, the accuracy of the data generated under these circumstances is suspect because of the unfamiliar environment and physically uncomfortable circumstances in which the data is taken.
To eliminate the problems associated with "sleep labs", solid-state portable physiological monitoring systems have been developed for use in the patient's own environment.
One such system is available from Vitalog Corporation. The Vitalog system is a portable microcomputer which monitors information from up to eight physiological sensors. This information is processed and stored in on-board, solid-state memory for subsequent retrieval or display by a separate computer system.
The Vitalog system contains an eight-channel analog-to-digital interface and an R-wave detector. The multichannel A/D converter samples eight analog inputs. A one-channel motion sensor composed of an array of omnidirectional mercury tilt switches detects patient movement. A one-channel electrocardiogram (ECG) signal is monitored using three standard ECG electrode pads. The amplified ECG signal is connected to an A/D channel and also to the R-wave detection circuit. A temperature sensor array monitors three channels of temperature using standard probes. Either one or two channels of respiration may be monitored. One channel can be programmed to monitor a patient response button.
When the Vitalog system is activated, its ROM-based operating system continuously monitors the sensor inputs. After each programmed monitoring period, information relating to heart rate, physical activity and temperature is stored. A running mean of normal R--R intervals is calculated at the end of each heart beat. At the end of each monitoring period, the current mean is encoded into one of 16 levels (4 bits) and stored. A filtered output count from the motion sensor is accumulated and encoded into one of 8 levels (3 bits). Temperature information is encoded using a 3-bit tracking scheme.
The Vitalog system can store data from a minimum of 3600 epochs. Data compression is used to ensure that no memory is used when data is unchanging.
A fundamental shortcoming of the Vitalog system is that it lacks individual event resolution. That is, because data gathered over a full monitoring period must be stored in limited on-board memory for retrieval at the end of the monitoring period, the data must be compressed prior to storage. This requires pre-storage processing according to a predefined algorithm, further limiting the stored data characteristics to rigid identifying and modifying signatures, thus reducing analytical flexibility
Thus, while the Vitalog system provides a screening tool, it does not address the need for a low cost, reliable, portable physiological data recording system which provides high data resolution for a number of parameters over long periods of time.